Embodiments of the invention relate generally to diagnostic imaging and, more particularly, to a method and apparatus of computed tomography (CT) imaging capable of having high temporal resolution, reduced image artifacts due to missing data and longitudinal truncation, and reduced radiation dose.
Typically, in computed tomography (CT) imaging systems, an x-ray source emits a fan-shaped beam toward a subject or object, such as a patient or a piece of luggage. Hereinafter, the terms “subject” and “object” shall include anything capable of being imaged. The beam, after being attenuated by the subject, impinges upon an array of radiation detectors. The intensity of the attenuated beam radiation received at the detector array is typically dependent upon the attenuation of the x-ray beam by the subject. Each detector element of the detector array produces a separate electrical signal indicative of the attenuated beam received by each detector element. The electrical signals are transmitted to a data processing system for analysis which ultimately produces an image.
Generally, the x-ray source and the detector array are rotated about the gantry within an imaging plane and around the subject. X-ray sources typically include x-ray tubes, which emit the x-ray beam at a focal point. X-ray detectors typically include a collimator for collimating x-ray beams received at the detector, a scintillator for converting x-rays to light energy adjacent the collimator, and photodiodes for receiving the light energy from the adjacent scintillator and producing electrical signals therefrom.
Typically, each scintillator of a scintillator array converts x-rays to light energy. Each scintillator discharges light energy to a photodiode adjacent thereto. Each photodiode detects the light energy and generates a corresponding electrical signal. The outputs of the photodiodes are then transmitted to the data processing system for image reconstruction.
One of the key modern applications for CT imaging is its use in cardiac imaging. However, cardiac imaging techniques such as coronary CT angiography pose unique technical challenges, one of which is the need for high temporal resolution to avoid motion artifacts in the image. One way to achieve such high temporal resolution is to use wide-coverage multi-detector-row CT (MDCT) systems to scan the entire heart region within one gantry rotation. Here, the wide coverage refers to the x-ray beam coverage in the longitudinal direction, which can cover the majority of the human's heart within one axial rotation. Typically, only data from roughly half of the scan is utilized for image reconstruction to maintain the temporal resolution. Unfortunately, however, such cardiac half-scan imaging methods face severe missing data and longitudinal truncation issues when the large x-ray cone beam angle is large. The cone beam artifacts caused by this cardiac half-scan method are easily observed in the reconstructed images and greatly deteriorate the image quality.
In order to mitigate the missing data and longitudinal truncation problems associated with the cardiac half-scan technique described above, the use of wide-coverage, full-scan cardiac imaging (albeit using a half-scan reconstruction method) is one solution. This wide-coverage, full-scan cardiac imaging offers a way to maintain temporal resolution while alleviating the missing data and longitudinal truncation problems associated with half-scan imaging. However, full-scan cardiac imaging imposes a larger radiation dose on the subject as compared to half-scan cardiac imaging. In fact, the radiation dose in full-scan cardiac imaging represents a 50 percent (or greater) increase in radiation dose over half-scan cardiac imaging. With every effort made to minimize the radiation dose and scan time to which the patient is subjected, conventional full-scan cardiac imaging is less than ideal.
Therefore, it would be desirable to design an apparatus and method for CT imaging capable of having high temporal resolution, reduced image artifacts due to missing data and longitudinal truncation, and reduced radiation dose.